The Yilgarn Craton forms the bulk of Western Australia and is home to 30% of the world’s gold deposits. Within in this region, the Laverton district is one of the most important gold producing regions. Underground miners of these “nuggety” gold deposits are under significant pressure to reduce their all in sustaining costs (AISC) and improve their return. Combine each mine’s sharp focus on costs with an extremely competitive diamond drilling market, and the result is the constant search for higher productivity in underground diamond drilling.

Using patented technology, the new Longyear bits have diamonds that are chemically bonded to the matrix creating a more versatile, faster penetrating, and a longer-lived bit. The new Longyear bits retain the smooth drilling characteristics drillers prefer, resulting in more core in the box on every shift for every crew. Available in 16mm more open, express geometry for even higher cutting speeds as well as 16mm Stage and 25mm Stage 3 configurations.

23% Increase in Meters Drilled/Hour

“Just some feedback… the other night I witnessed a bit cutting 24 inches a min … by far the fastest cutting bit Boart Longyear has made…” Boart Longyear Site Supervisor, Western Territory.

The Challenge

On the surface, the Laverton district is a flat, hot, dry environment with scattered acacia trees only interrupted by dry, salt lake beds, and gypsum sand dunes. The high concentration of salt results in a very saline aquifer. While the high salinity is hard on equipment it does not factor heavily into bit selection and drilling performance.

Within this host rock, the gold is typically contained within intrusive dykes of quartz porphyry near the shear and fracture networks which supported gold-bearing hydrothermal flow. The greenstone, shale and even basalts are only of medium hardness and have the potential to be cut quite quickly, while the sections of BIF, quartz and fracture zones force slower penetration rates. The ideal bit would be versatile; free-cutting enough to easily handle the occasional BIF and quartz but tough enough to penetrate the greenstones quickly.

The underground portion of the mine is decline accessed and extends 900m below the original open pit. Due to its “nuggety” deposit, diamond drilling tends to underestimate grade, so the mine has adopted new techniques of grade control. RC drilling has been introduced underground to produce larger sample volumes, which match well with the bulk mining techniques being used. Considering that RC drilling is typically half the cost-per-meter and three times faster, and the industry-wide initiatives to drive down all in sustaining costs, a lot of scrutiny is paid to the productivity of remaining diamond drilling.

After optimizing drilling parameters, the incumbent product’s (Hayden 9AA and KS5) average performance, maxed out at 180 meters/bit life and 22 centimeters/min of penetration rate over the three months of monitoring. While solid performance, a new solution was needed to continue improving productivity.

The Solution

The first step was to introduce the new Longyear™ Green Bit in a Stage™ 3 25mm configuration. The Longyear Green formula (Prototype P520) was selected to drill like the competitor’s 9AA formula with Stage configuration to maximize life. Comparing performance in the three-month period after adoption, penetration rate increased to 26 centimeters/minute and bit life nearly doubled, increasing to 356 meters/bit. The ease of use and consistency across shifts was appreciated by the crews and helped produce the measurable gain. These improvements combined to noticeably increase core in the box by 6%. The Boart Longyear drill crews correctly observed that such long life was not driving a significant increase in productivity as reduced tripping time has less impact than improved penetration, so the decision was made to trial even more free-cutting formulas.

The next bit trialed was the Longyear Yellow (Prototype P575) again in the Stage 3 25mm configuration to line up against the competitor’s KS5 and even 12-14. The penetration rate jumped to an average of 35 centimeters per minute and life held at an impressive 300 meters per bit. Since the bits were still achieving much better life, Boart Longyear Drilling Services moved one more step up to the Longyear Red bit (Prototype P566). Since the goal was to maximize penetration rate, the Longyear Red bits were produced in the 16mm express configuration with a more open area for enhanced penetration.

The Longyear Red bits achieved an astonishing 60 centimeters per meter penetration rate and still lasted 120 meters. With the goal of maximizing productivity, the drill crews decided to use one Longyear Red at the top of the hole and finish it with a Longyear Yellow in 25mm Stage 3. The results speak for themselves. After 3 months of measurement, this two-bit strategy averaged 283 meters/bit, still a 60% improvement over the competition and 34 centimeters per minute, a full doubling of penetration rate. The combined result put 23% more core in the box.

Express Geometry

With the competitiveness of today’s market, everyone is looking to cut faster, especially underground. To support higher penetration rates, we have combined the new Longyear™ formulas with a new, more open express geometry. Tapered intermediate waterways improving flushing and prevent accumulation of debris. Designed for fast cutting in competent ground, the new express geometry is available in our 16mm crown heights to maintain bit life at higher cutting speeds.

After the promising initial results, trials were started using the new Longyear bits on all Boart Longyear Drilling Services sites in Australia and select sites globally. Now, all sites in Australia have converted to great effect on productivity. Over the next six months, the new Longyear bits in the Longyear line will be launched, moving from prototype to full production. Longyear bits are now stocked in Australia and available to order.

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MEET THE AUTHORChris LambertChris Lambert has a bachelor’s degree in mechanical engineering and has been with Boart Longyear since 2008. He has been the company’s global product manager for coring tools, including rods, in-hole tools and diamond bits, since 2012. Prior to that, he was the engineering manager for diamond products. His 20-year engineering and product development career has included materials, hydraulics, pumps and diesel engines.

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